U.S. Pat. Nos. 4,751,530, Elrod et al, 4,751,534, Elrod et al, and 4,751,529, Elrod et al, assigned to the assignee of the present application, disclose printheads for acoustic ink printers, wherein an acoustic transducer is deposited or otherwise coupled to the lower surface of a substrate, and a concave lens is formed in the opposite surface of the substrate. The lens, which may have a quarter wave impedance matching layer to avoid the reflection of waves back to the transducer, focuses the acoustic beam at a point near the surface of an ink pool adjacent the upper surface of the substrate. The transducer in these arrangements may comprise a piezoelectric element sandwiched between a pair of electrodes, to excite the piezoelectric element into a thickness mode oscillation. Modulation of RF excitation applied to the piezoelectric element causes the radiation pressure, which the focused acoustic beam exerts against the upper surface of the pool of ink, to swing above and below a predetermined droplet ejection threshold level as a function of demand.
In acoustic ink printers, crosstalk due to near field diffraction of nominally planar sound waves, in a typical substrate, can adversely affect ejection stability and precision. As an example, in a typical structure employing a 1.5 mm thick transducer with a radius of 340 .mu.m, intensity crosstalk due to near field diffraction is computed to be 3.7%. This is a substantial fraction of the acoustic ink printer 10% power regulation, within which it is desired to maintain the power, and can noticeably contribute to crosstalk.
Acoustic ink printheads are also disclosed, for example, in U.S. Pat. No. 4,719,476, Elrod et al, U.S. Pat. No. 4,719,480, Elrod et al, U.S. Pat. No. 4,748,461, Elrod, U.S. Pat. No. 4,782,350, Smith et al, U.S. Pat. No. 4,797,693, Quate, and U.S. Pat. No. 4,801,953, Quate, each of which is also assigned to the present assignee.